Hydraulic pump and control



J. s. cARDlLLo ET AL HYDRAULIC PUMP AND CONTROL Nov. 6, 1956 3 Sheet-Shee 1 Filed March 23, 1951 Nov. 6, 1956 J. s. cARDlLLo ET Al. 2,769,393

HYDRAULIC PUMP AND CONTROL 3 Sheets-Shee 2 Filed March 23, 1951 nMHcwzm l W Nov. 6, 1956 J. s. cARDlLLo ET AL HYDRAULIC PUMP AND CONTROL 3 Shee'ts-Shee 5 Filed March 23, 1951 United States Patent Oiitice 2,769,393 Patented Nov. 6, 1956 2,769,393 HYDRAULIC PUMP AND CONTROL Joseph S. Cardillo and Melvin M. Hann, Rockford, Ill.,

assignors to Sandstrand Machine Tool Co., a corporation of Illinois Application March 23, 1951, Serial No. 217,258 11 Claims. (Cl. 103-5) This invention relates to a hydraulic pump and more particularly to a wobbler or swash plate type hydraulic pump.

It is the general object of this invention to produce a new and improved hydraulic pump.

It is a more specific object of this invention to produce a hydraulic pump of the type having a cylinder block provided with a plurality of annularly arranged parallel cylinders, with pistons in the cylinders adapted to be reciprocated by relative motion between the block and a tiltable swash plate or wobbler and to provide such a pump with means for urging the pistons in the direction of the wobbler or swash plate.

Another object of the invention is to provide a pump of the type described in the preceding paragraph with spring means connected to the outer ends of the pistons to urge the pistons outwardly against the wobbler or swash plate.

A further object of the invention is to produce a piston type pump provided with springs surrounding the outer ends of the pistons, each spring having one end bearing against a piston and the other end supported on a member freely movable into parallel relationship with the wobbler or swash plate.

A further object of the invention is to produce a rotating barrel axial piston wobbler or swash plate type pump provided with means for insuring complete lling o-f the cylinder on each intake stroke of the pistons.

Another object of the invention is to produce a piston type hydraulic pump having means for increasing the pressure at the inlet side of the pump to aid in the complete lling of the cylinders with iluid to be pumped on each intake stroke of the pistons.

A further object of the invention is to produce a piston type hydraulic pump provided with an inlet chamber connected to the inlet side of the pistons and to provide such chamber with a centrifugal impeller rotated during operation of the pump to increase the pressure on the inlet side of the pump.

A further object of the invention is to produce a piston type hydraulic pump or motor having passages connected to the inlet side of the pistons of the cylinders so shaped as to provide `a smooth streamlined passage through which the incoming oil may enterand completely fill the cylinder cavities.

It is another object of the invention to produce a rotating barrel piston type hydraulic pump or motor having a plurality of passages opening to the inlet of the cylinders and curved in the direction of rotation of the cylinder block; said passages being curved so as to lie substantially along the path of motion of the fluid to be pumped relative to the cylinders, said path being the resultant of the axial speed of the uid and the circumferential speed of the cylinders.

Another object of the invention is to produce a hydraulic pump or motor having new and improved lubricating and cooling means.

Another object of the invention is to produce a hydraulic pump or motor provided with pressure producing means for causing a forced feed of lubricating oil into vthe casing and including a priming valve in the lubricating oil circuit serving to vent air entrained in the lubricating oil to outside of the casing.

A further object of the invention is to produce a hydraulic pump or motor of the type described in the two preceding paragraphs which is provided with means for preventing drainage of lubricating oil from the casing in the event of failure of the source of lubricating oil.

A further object of the invention is to produce a control for maintaining the output pressure of a hydraulic pump substantially constant and at a predetermined level.

A further object of the invention is to produce a control for a hydraulic pump of the rotating barrel axial piston wobbler or swash plate type which includes a control piston contacting the wobbler or swash plate for tilting the same to various positions together with a pilot valve which senses output pressure of the pump and directs pressurized oil to or from the piston as required to maintain pump pressure at a predetermined level.

Other and further objects of the inventio-n will be readily apparent from the accompanying drawings, in Which:

Fig. 1 is a longitudinal sectional view through a hydraulic pump embodying the invention and taken substantially along line 1 1 of Fig. 2;

Fig. 2 is a vertical transverse section taken along line 2 2 of Fig. l;

Fig. 3 is a vertical section taken along line 3 3 of Fig. l;

Fig. 4 is an enlarged detail view of the casing drain valve taken along line 4 4 of Fig. 3;

Fig. 5 is a sectional view of the priming valve taken along line 5 5 of Fig. 3;

Fig. 6 is a vertical transverse section taken along line 6 6 of Fig. l;

Fig. 7 is an arcuate section taken along curved line 7 7 of Fig. 6; and

Fig. 8 is a diagrammatic view of the actual and apparent velocities of uid to be pumped as introduced into the n cylinders and the direction of rotation of the cylinders.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one specic embodiment, with the understanding that the present disclosure is to be considered as an exemplication of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be poined out in the appended claims.

Referring now to Fig. l of the drawings, there is shown a casing 10 enclosing a rotatably mounted cylinder block 11 with the block being provided with a plurality of cylinders 12 housing pistons 13 which are reciprocated by means of a non-rotating tiltable swash plate 14.

The cylinder block 11 is driven by mea-ns of a drive shaft 15 and the position of the swash pla-te is determined by the means of a control system 16. The right-hand end (as seen in Fig. l) of the casing is closed by an end plate 20 to which is secured an annular ring member 21 supporting an anti-friction bearing 22 which in turn rotatably supports one end of the drive shaft 15. The other end of the casing is closed by an end plate 23 which supports a bushing 24 rotatably supporting the opposite end of the drive shaft 15. The end plate 23 is provided with a recess 24 forming an annular inlet chamber which is closed by a cover plate 25 secured to the end plate 23 by `the bolts 26.

The cylinder block 11 is splined to the drive shaft 15 at 30 as shown. The cylinders 12 are in turn splined to the block at 31. The block is provided with two annular flanges 32 and 33 each provided with a plurality of holes 34 and 35 aligned with the cylinders 12 in each aligned two of which there is reciprocatorily mounted a push rod 36. The left-hand end of each of the push rods is reduced in diameter and threaded as indicated at 40, and a nut 41 engages the threads to secure the piston to the end of the push rod.

Although in the particular embodiment of the invention chosen for purposes of illustration the pistons 13 are of larger diameter than the push rods 36 and the push rods themselves are contained within the holes 34 and 35, it will be obvious to those skilled in the art that the invention is equally applicable to hydraulic pumps or motors in which unitary cylinders extend from end to end of the block and in which the pistons and push rods are integral structures extending from end to end of the cylinders. Accordingly, in the following description and claims the combination of the cylinders 12 and the holes 34 and 35 may be referred to generally as cylinders and the pistons and push rod assemblies may be referred to simply as pistons reciprocable in the cylinders.

The swash plate 14 is tiltably mounted upon the trunnion bearings 50 secured in the casing and is provided with a face 51 to contact and reciprocate the pistons. The swash plate 14 does not rotate with rotation of the block but remains stationary and the angle to which the swash plate is tilted relative to the axis of rotation of the block determines the length of the stroke of the pistons and hence the displacement of the pump.

A spring supporting member 52 encircles the drive shaft 15 within the casing and is rockably seated in a semi-spherical recess 53 formed in the right-hand end of the cylinder block. The spring supporting member comprises an annular collar 54, the outer ends of which seat in the recess 53, and an integral ange 55 which extends radially from the collar. A plurality of semi-spherically shaped openings S6 are provided about the periphery of the flange 55, each of the openings surrounding one of the pistons. A spring seat 57 is provided with a semispherical face seated in the semi-spherical opening 56 against which a spring 58, one of which surrounds each of the pistons, bears. The other end of each spring bears against an integral shoulder portion 59 formed in the outer ends of the pistons.

A semi-spherical socket 60 is formed in the outer end of the pistons in which a slipper in the form of a ball member 61 is seated. Each ball member 61 is provided with a flat face 62 bearing against the face 51 of the swash plate to establish the contact between the swash plate and the pistons.

A plurality of radial passages 63 are formed in each end face 62 and communicate at their outer end with an annular groove 63 and at their inner end with a passage 64 which latter passage is in communication at all positions of the member 61 with a passage 66 extending longitudinally through the piston and opening at its other end to the cylinder 12. The passages 63 and the annular groove 63 are subject to the discharge pressure of the purnp and serve to relieve a portion of the pressure existing between the face 62 of the ball member and the face of the wobbler. Leakage of uid under discharge pressure between the faces of the ball member and swash plate produces a substantially linear pressure gradient across the face 62, being discharge pressure at the inner edge of the face and case pressure at the outer edge. The area 62 is so proportioned that the pressure across the face is approximately 90% of the discharge pressure in the left-hand or pumping end of the piston. Thus only of the discharge pressure on the pistons is actually berne by the faces 51 and 62. Clearly, the area 62 could be so proportioned as to produce a greater or lesser percentage of load distribution. Furthermore, fluid leaking past the face 62 serves to lubricate the contact between that face and the face of the swash plate.

It will be noted from the foregoing descrip-tion that the spring supporting member 52, while fixed for rotation with the cylinder block, is freely rockable on the block so that it may assume a position parallel to the swash plate 14. The springs 53, which are compression springs, serve to urge the pistons outwardly in 'the direction of the swash plate. Thus a positive preload is independently applied to each piston in the direction of the swash plate and eliminates any possibility of back lash resulting from Vany tolerance build-up in any one or several of the mating parts of the entire assembly. The spring supporting member 52 acts simply as a support for each of the several return springs 58 and remains parallel to the wobbler at all angular settings. Therefore, each of the springs exerts outward pressure on its associated piston without the springs being extended or compressed during operation of the device, thus decreasing the fatigue characteristics and improving the life of the springs.

Referring now to Figs. l, 2 and 3, the pump is provided with an inlet 7i) opening in-to the recess 24 and an outlet 71. As previously pointed out, the recess 24 is annular in shape, but as will be noted from Fig. 2, is eccentric to the axis of the drive shaft 15. A plurality of inlet passages 72 are provided in the end plate 23 and open to the recess 24 in the portion furthest removed from the axis of rotation of the drive shaft. An arcuate intake port '74 is formed in an intake port plate 75 fixed in the casing 10 and communicates with each of the inlet openings 72.

An impeller '.76 of the multi-blade, backward pitched, centrifugal type is fixed to an extension 77 of the drive shaft to be rotated thereby in order to provide pressurized fluid to the piston inlet ports during high speed, low inlet pressure operations. As the drive shaft is rotated the impeller 76 is rotated therewith and serves through centrifugal action to create a head of pressure within the recess or chamber 24;. During high speed operation the action of the impeller in creatirg pressure in the inlets of the pump assures that all of the cylinders will be till-ed with tiuid during each stroke of the pistons. Incoming fluid is directed by centrifugal action into the recess 24 surrounding the impeller, fluid leaving the inipeller imparting its kinetic energy in the form of head pressure against the surrounding port housing. .in order to discourage high speed rotary motion of the fluid within the recess 24., there is provided a tlow blocking means in the form of a pin 7S located within the recess. The pin serves to break up the rotary flow in the recess which would otherwise occur.

Fluid pumped by the pistons is directed into an arcuate discharge port 79 and thence into the outlet 71.

Each of the cylinders i2 terminates in a constricted passage @il which communicates alternately with the intake port 74 and the discharge port 79' as the cylinder block is rotated. in order to eliminate entrance shock and the tendency for cavitation at high speeds and high inlet suction conditions, the passages Si@ are curved or bevelled and are also elongated. As best seen in Figs. 6 and 7, the passages St) are curved in the direction of rotation of the cylinder block. When the cylinder block is driven so as to affect the pumping operation the curved or bevelled elongated passages S9 leading into the cylinder cavities do not tend to scoop fluid out of the arcuate port 74 but instead present themselves so as to form a natural streamlined passage through which the incoming uid may enter the cylinder cavity. Thus incoming uid on the cylinder Wall is directed in a natural streamlined manner into the entire cylinder' cavity insuring at the same time a completely filled cavity.

The particular shape of the curvature or bevclling of the passages 8) may best be determined by a correlation between the motion of fluid moving through the arcuate port 74 and the speed direction of rotation of. the cylinders. Referring to Fig. 8 if the line a bc taken to represent by its direction the direction of rotation of the cylinders and by its length the speed of rota 'on of the cylinders and the direction and length of the line b as indicating the speed and direction of movement of the incoming iiuid, the resultant c is the speed and direction of movement of the incoming oil relative to the cylinders. The passages 8G are bevellcd or curved so as substantially to parallel the line c and thus to provide an inlet int-o the cylinders which is substantially parallel to the direction of movement of incoming -oil relative to the cylinders.

Hydraulic pumps or motors of the rotating barrel, axial piston wobbler or swash plate type are usually employed to pump a fluid which possesses lubricating properties. In such cases, lubrication of the moving parts within the casing may be achieved by directing a portion of the fluid pumper into the casing. It has been customary to provide such casing with a drain opening leading to a sump or tank for draining the fluid from the casing to provide a constantly fresh supply of lubricant. This system, while simple, possesses a number of disadvantages and dangers. For example, should the pump discharge be blocked for any reason the pump may continue to operate at maximum discharge pressure without flow from the discharge port. With no flow of oil from the discharge port, the source of lubricating oil is lost and drainage from the casing results in a dry casing with consequent damage to the moving parts. Further, during extended periods of operation with a blocked or disconnected inlet line, the normally contained oil in the casing is displaced by air moved by the pump, resulting again in a dry condition and damage to the pump.

According to this invention, there is provided lubrieating means wherein lubricant from the inlet is directed under pressure into the case for lubricating the moving parts therein, there being a priming valve in the lubricating circuit for venting air to the atmosphere rather than admitting it into the casing and there also being a pressure responsive valve closing the drain means for the casing, the last named valve operating to maintain the casing closed against drainage except under conditions where fresh lubricant is being supplied thereto.

Referring to Fig. 1, there is shown a passage '90 which connects the main pump inlet to the intake side of a gear pump 91 fixed to the outer extremity of the extension 77 of the drive shaft and mounted within the cover plate 25. The discharge side of the gear pump is connected by a passage 92 to a port in an annular groove 93 formed in a sleeve 94 of a priming valve 95 (Fig. 3). Also formed in the sleeve 94 is a second port in the form of an annular groove 96 and a third port in the form of a groove 97. The port 96 connects with a passage 98 (Fig. 1) which leads into the interior of the casing 10. The port 97 connects with a separate passage 99 which is vented through the drain plug 100 to the' exterior of the casing.

Slidable within the bore is a piston valve 101 constantly urged to the left (as seen in Fig. by a spring 102. The left-hand end of the piston valve, as seen in that figure, is provided with a reduced portion 103 which, with the sleeve 94, forms a chamber 104 within the lefthand end of the sleeve. Communication between the chamber and the port 93 is obtained by means of an opening 105 in the annular groove 93. Extending longitudinally through the piston valve is a passage 106 which opens at one end to the chamber 104 and connects at its other end with an annular groove 107 adapted to be moved into communication with the annular groove 97 through an opening 108 therein.

When the pump is first started, air and oil are pumped into the passage 92 by the gear pump 91. Air entering the chamber 104 is drawn off through the passage 106, annular grooves 107 and 97, and passage 99, and thereby vented exterior of the casing. When the pump 91 is pumping liquid, the pressure buildup within the chamber 104 is sufficient to overcome the biasing effect of the spring 102 to shift the piston valve 101 to the right against the spring, interrupting communication between the annular grooves 107 and 97 and establishing' communication with the chamber 104 and the annular groove 96 to direct oil under pressure into the casing. From the casing the oil travels through a drain passage 110 and out through the drain plug 100.

As can best be seen in Fig. 4 a pressure responsive valve 111 is provided to s'hut off communication between the drain passage 110 and the drain port, the valve in- 6 cluding a ball member 112 seated on a movable piston' like memberk 113 which is urged into sealing relationship with the drain passage by a spring 114. Normal liquid pressure within the casing and produced by the gear pump 91 is suicient to lovercome the tension of the spring 114 and to permit the ball and piston 112 and 113 to move downwardly, as seen in Fig. 4, establishing communication between the drain passage and the drain port. Should at any time there be a failure of lubricating oil supply, so that the pump 91 is moving air rather than oil, two things occur. In the first place, the pressure drop within the casing 10 permits the spring 114 to close the valve 111 thereby preventing drainage of oil from the casing. Secondly, the pressure within the chamber 104 of the priming va-lve 95 drops permitting the spring 102 to shift the valve to the position shown in Fig. 5 to vent air moved by the pump exteriorly of the casing. In this manner the oil supply within the casing is not depleted.

Under normal operating conditions a constant stream of fresh oil is introduced into the casing and drained therefrom. Such constant movement of lubricating oil serves not only to provide better lubrication under cleaner conditions but also serves to cool moving parts of the pump within the casing.

The control means system 16 previous-ly referred to is adapted to maintain the output pressure of the pump at a predetermined level. For accomplishing the regulation of the pump, the device includes a control piston reciprocable wit-hin a cylinder 121 which extends parallel to but spaced from the axis of rotation of the cylinder block 11. Within the control cylinder is a spring 122 which biases the control piston outwardly in the direction of the swash plate 14. The strength of the spring 122 is such as to move the swash plate into maximum stroke position when the pump is at rest, the swash plate being tilted as shown in Fig. 1 until the side opposite the side contacted by the control piston comes to rest against pin 123 fixed in the case. It will be noted that the trunnion'axis 50 of the swash plate 14 is located slightly above the axis of the shaft 15. This produces a pressure moment on the swash plate when the pump is operating which biases the wobbler to a no-stroke position, the force being amply `sufficient to overcome the strength of the spring 122. Thus if the spring alone were utilized to shift the swash plate it would move it into maximum stroke position when the pump is at rest but as the pump started the .pressure forces exerted on the swash plate by reason of its off center axis would move the swash plate to a no-stroke position.

Located in spaced parallel relationship to the cylinder 121 is a control valve having a bore 125 in which a control piston 126 is reciprocable, the piston being urged to the leftmost position in the bore by a compression spring 127. The cylinder 121 is connected by a passage 128 to a port 129 in the bore. A second passage 130 connects at one end to a port 131 in the bore and at the other end to the discharge port of the pump, thus subjecting the bore to the discharge pressure generated. A drain passage 132 opens t0 the bore for draining fluid therefrom. The control valve 126 terminates at its left-hand end in a reduced portion 133 which forms a piston reciprocable in a correspondingly reduced portion 134 at the left-hand end of the bore. A fluid conduit 135 drilled longitudinally through the piston valve 126 connects the cylinder 134 with an annular groove 136 defined between two lands 137 and 138 on the valve. To effect this connection a passage 139 is drilled through the annular groove 136 to connect with the conduit 135. A second fluid conduit 140'is drilled axially through the piston valve and opens to an annular groove 141 deferred between a land 142 and land 138. The annular groove 141 may be moved into a position communicating with the drain passage 132 to exhaust fluid from the cylinder 134.

A second longitudinal conduit ,143 extends longitudinally through the piston valve 126 which opens to each end thereof as shown. Intermediate its ends, the passage 143 connects to the drain groove 142. Means in the form of an adjustment screw device 144 is provided for adjusting the tension of the spring 127.

The operation of the control is as follows. As previously stated the spring 122 is sufficient to move the swash plate to the maximum stroke position shown in Fig. l under start-up conditions. As the pump is started discharge pressure is immediately sensed by the passage 131i which directs the pressure through the port 131 and into the bore 125. From the bore 125 discharge pressure is directed to the port 129 and passage 128 and into the control cylinder 121 to maintain the piston 120 in the maximum stroke position shown against the increasing tendency of the swash plate to move to a 11o-stroke position.

Fluid under pressure is also directed through the passage 139 and iluid conduit 13S to the small cylinder 134 at the left-hand end of the bore. When the discharge pressure has reached a level predetermined by the setting of the adjustment device 146i` it overcomes the tension of the spring 127 to shift the pilot valve 126 to the right to the position shown in Fig. l. As discharge pressure continues to increase the piston valve is shifted rightward from the position shown in Fig. l to bring the land 13S to a position partially blocking the port 131. At the same time rightward movement of the land 138 establishes communication between the passage 12d and the drain line 132 to permit drainage of fluid from the control cylinder, an equilibrium condition may thus be established to maintain the wobbler in a fixed position. Should at any time the discharge pressure increase, further movement of the piston valve 126 in response to the increase of pressure in the cylinder 134 completely blocks the port 131 While further opening the cylinder 121 to the drain to permit the control piston 120 to shift to the left reducing the stroke. As previously stated the left- Ward movement of the control piston 120 is affected by the swash plate itself because of its above centerline mounting. lf on the other hand the discharge pressure should drop below the desired amount there Will be a corresponding drop in the pressure delivered to the small cylinder 13d permitting the spring 127 to shift the pilot valve leftware'- reestablishing communication between the discharge pressure port 131 and the passage 128 to pressurize the control cylinder 121 moving the control piston to the right. Any fluid leaking past the lands in the pilot valve Which might effect movement of the valve is drained to the case by the passage 142 which connects with the longitudinal passage 143.

We claim:

l. In a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly arranged in the block, a piston reciprocable in each cylinder, a swash plate positioned to contact the ends of the pistons for moving the pistons in the cylinders and angularly movable to vary the stroke of the pistons, and a drive shaft operatively connected to rotate the block relative to the swash plate, spring return means for the pistons comprising a semi-spherical recess formed in the end of the block adjacent the swash plate, a spring supporting member ha 7ing an annular ilange rockably received in the recess and a second annular ilange extending substantially at right angles to the iirst flange, a plurality of semi-spherical openings in the second flange each surrounding a different one of the pistons, a spring seat having a semi-spherical base positioned in each opening, and a plurality of Compression springs each encircling a dierent one of the pistons and having one end seated in a spring seat and having its other end secured to the piston for urging the piston in the direction of the swash plate.

2. In a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly arranged in the block, a piston reciprocable in each cylinder, a

swash plate positioned to contact the ends of the pistons for moving the pistons in the cylinders and angularly movable to vary the stroke of the pistons, and a drive shaft operatively connected to rotate the block relative to the swash plate, spring return means for the pistons comprising a semi-spherical recess formed in the end of the block adjacent the swash plate, a spring supporting member having an annular flange rockably received in the recess and a second annular flange extending substantially at right angles to the rst llange, a plurality of semispherical openings in the second flange each surrounding a different one of the pistons, a spring seat having a semispherical base positioned in each opening, a plurality of compression springs each encircling a different one of the pistons and having one end seated in a spring seat and having its other end secured to the piston for urging the piston in the direction of the swash plate, a socket on the outer end of each piston and a ball member in the socket having a face bearing against the swash plate.

3. In a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly arranged in the block, a piston reciprocable in each cylinder, a swash plate positioned to contact the ends of the pistons for moving the pistons in the cylinders and angularly movable to vary the stroke of the pistons, and a drive shaft operatively connected to rotate the block relative to the swash plate, spring return means for the pistons comprising a spring supporting member surrounding the drive shaft and rockably mounted on the block, a plurality of semi-spherical openings in the member each surrounding a different one of the pistons, a spring seat having a semi-spherical base positioned in each opening, a plurality of compression springs each encircling a different one of the pistons and having one end seated in a spring seat and having its other end secured to the piston for urging the piston in the direction of the swash plate, a socket on the outer end or" each piston, and a ball member in the socket having a face bearing against the swash plate.

4. in a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly arranged in the block, a piston reciprocable in each cylinder, a swash plate positioned to Contact the ends of the pistons for moving the pistons in the cylinders and angularly movable to vary the stroke of the pistons, means on the ends of each of said pistons engaging the swash plate, and a drive shaft operatively connected to rotate the block relative to the swash plate, spring return means for the pistons comprising a spring supporting member surrounding the drive shaft, a plurality of semi-spherical openings in the member each surrounding a different one of the pistons, a spring seat having a semi-spherical base positioned in each opening, and a plurality of compression springs each encircling a different one of the pistons and having one end seated in a spring seat and having its other end secured to the piston for urging the piston in the direction of the swash plate, said spring supporting member being rockably mounted on the block whereby it may be retained by said springs in a position parallel to the swash plate.

5. In a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly arranged in the block, a piston reciprocable in each cylinder, a swash plate positioned to Contact the ends of the pistons for moving the pistons in the cylinders and angularly movable to vary the stroke of the pistons, means on the ends of each of said pistons engaging the swash plate and a drive shaft operatively connected to rotate the block relative to the swash plate, spring return means for the pistons comprising a spring supporting member surrounding the drive shaft, a plurality of openings in the member each surrounding a different one of the pistons, and a plurality of compression springs each encircling a different one of the pistons and having one end supported by the sides of one of the openings and having its other end secured to the piston for urging the piston in the direction of the swash plate, said spring supporting member being rockably mounted on the block whereby it may be retained by said springs in a position parallel to the swash plate.

6. In a hydraulic pump or motor having a cylinder block, a plurality of parallel cylinders annularly Aarranged in the block, a piston reciprocable in each cylinder, a motion converting device positioned to contact the pistons for moving the pistons in the cylinders, and means on the end of each of the pistons engaging the motion converting device, said motion converting device being movable to vary the stroke of the pistons and said block 'and said motion converting device being mounted for rotation relative to each other, spring return means for the pistons comprising a spring supporting member mounted on the block to be freely movable into parallel relationship with the motion converting device in all positions thereof, said member being provided with an opening about each of the pistons, means dening a spring seat at the sides of each opening and a plurality of springs each encircling a different one of the pistons and having one end seated in a spring seat and having its other end secured to the piston for constantly urging the piston in the direction of the motion converting device.

7. Ina hydraulic pump or motor having a plurality of annularly arranged parallel cylinders, a piston reciprocable in each cylinder, a motion converting device positioned to contact the pistons for moving the pistons in the cylinders and means on the end of each of the pistons engaging the motion converting device, with the cylinders and said motion converting device being mounted for rotation relative to each other, spring return means for the pistons comprising a rockably mounted spring supporting member provided with a plurality of spring seats, and a plurality of springs each having one end seated in a different spring seat and having its other end secured to a different piston for constantly urging the pistons in the direction of the motion converting device.

8. In a rotating barrel axial piston type pump having a drive shaft for rotating the barrel, and a casing enclosing the pump, means for pressurizing pump intake comprising an end plate closing one end of the casing, means including the end plate dening an annular inlet chamber, an arcuate intake port opening to the cylinders of the pump on their intake strokes, a plurality of separate intake passages each opening at one end to the periphery of the chamber and at its other end to the intake port, a pin projecting into said periphery of the chamber to interfere with rotary movement of fluid therein, a centrifugal impeller in the chamber and mounted on the drive shaft to be rotated thereby, and a suction port opening to the chamber at the inlet of the impeller.

9. A control for a swash plate type hydraulic pump comprising a cylinder, a control piston in the cylinder and contacting the swash plate, valve means for directing uid under pressure to the cylinder to move the control piston and the swash plate, said valve means including a bore, a member movable in the bore, resilient means at one end of the bore and biasing the member toward movement in one direction, a fluid conduit extending through the member and opening to the other end of the bore, a plurality of ports in the bore, a passage connecting one of the ports to the discharge of the pump, a second passage connecting another of the ports to the cylinder and a third passage connecting another port to a drain, means carried by the movable member and controlling the ports including an annular groove communicating with said uid conduit to subject said other end of the bore to pump discharge pressure to move the member against the resilient means.

10. A control for a swash plate type hydraulic pump comprising a cylinder, a control piston in the cylinder and contacting the swash plate, a spring in the cylinder urging the control piston in the direction of the swash plate, said spring being adapted to tilt the swash plate to maximum 10 stroke position when the pump is at rest, valve means for directing iluid under pressure to the cylinder to move the control piston and the swash plate including a bore, a

valve member movable in the bore, means at one end of the bore and biasing the member toward movement in one direction, means defining a cylinder at the other end of the bore, said last named cylinder having a diameter less than the diameter of the bore and extending coaxially therewith, a piston fixed to the valve member and reciprocable in said last mentioned cylinder, a fluid conduit extending through the member and said last mentioned piston and opening to said cylinder in the end of the bore, a plurality of sports in the bore, a passage connecting one of the ports to the discharge of the pump, a second passage connecting another of the ports to the cylinder and a third passage connecting another port to a drain, lands carried by the Valve member and controlling the ports and dening an annular groove communicating with said fluid conduit to subject said last mentioned piston to pump discharge pressure to move the member against the resilient means.

1l. A control for a rotating barrel axial piston swash plate type hydraulic pump comprising a control cylinder having its axis parallel to and spaced from the axis of rotation of the barrel, a control piston reciprocable in the control cylinder and contacting the swash plate, a compression spring in the control cylinder urging the control piston in the direction of the swash plate, said spring having sufficient strength to tilt the swash plate to maximum stroke position when the pump is at rest and insufficient strength to maintain the swash plate in a stroke-producing position when the pump is operating, valve means for directing fluid under pressure to the control cylinder to move the control piston and the swash plate, said valve means including a bore, a plurality of ports in the bore, a passage connecting one of the ports to the discharge of the pump, a second passage connecting another of the ports to the control cylinder, a third passage connecting another of the ports to a drain, a pilot valve slidable in the bore and provided with a plurality of spaced lands controlling the ports, a spring at one end of the bore and biasing the pilot valve toward movement in one direction, means defining a pilot valve cylinder at the other end of the bore, said pilot valve cylinder having a diameter less than the diameter of the bore and extending coaxially therewith, a pilot valve piston xed to the pilot valve and reciprocable in said pilot valve cylinder, a uid conduit extending through the pilot valve and the pilot valve piston and opening to said pilot valve cylinder and a passage connecting the fluid conduit to the space between two of said lands to subject said pilot valve cylinder to the discharge pressure of the pump whereby to move the pilot valve against said pilot valve spring to direct discharge pressure into said control cylinder or to connect said control cylinder with the drain in accordance with the position of the pilot valve.

References Cited in the ile of this patent UNITED STATES PATENTS Re. 21,758 Foisy Apr. 1, 1941 1,807,515 Drysdale May 26, 1931 2,115,121 Phillips Apr. 26, 1938 2,177,098 Doe et al. 0ct. 24, 1939 2,299,234 Snader et al Oct. 20, 1942 2,392,543 Mercier Jan. 8, 1946 2,404,309 Martin July 16, 1946 2,412,835 Robinson Dec. 17, 1946 2,417,137 Smith Mar. 11, 1947 2,453,266 Rockwell Nov. 9, 1948 2,458,452 Vanni Jan. 4, 1949 2,531,319 Briggs Nov. 21, 1950 2,543,624 Gabriel Feb. 27, 1951 2,556,426 Hoffer June 12, 1951 2,620,733 Overbeke Dec. 9, 1952 

